1. Field of the Invention
The present invention relates to a motion vector detection method and apparatus.
2. Description of the Related Art
Generally, an image display unit is classified roughly into an impulse type display that continues to emit light during afterglow time of fluorescent material after writing of image, and a hold model display that continues to display a previous frame till writing of image is performed afresh. There are a CRT display and a field emission type display (referred to as FED) in the impulse type display. There are a liquid crystal display unit (referred to as LCD) and an electroluminescence display (refer to as ELD) in a hold type display unit.
Problems of the hold type display are indistinct phenomena occurring in an image display. The occurrence of the indistinct phenomenon causes in that the images of a plurality of frames are piled up and projected on the retina when a moving object exists in the images over a plurality of frames, and the eyes of an inspection person followed the movement of the moving object.
A display image of a frame continues to be displayed until the display image is changed to that of a frame subsequent thereto. However, an operator is to observe the display image of the frame while predicting that of the frame subsequent thereto and moving the former display image in a moving direction of the moving object. In other words, the tracking motion of eyes of the operator has continuity, and the eyes allows sampling whose interval is shorter than the frame interval. The eyes are therefore casted on an image as if the image were formed between two adjacent frames. As a result, the image is observed as an indistinct image.
The shortening of the frame interval is preferable in order to solve the problem. It is conceivable as a concrete technique to perform interpolation between adjacent frames by forming an interpolation image using motion compensation used in MPEG (Motion Picture Experts Group) 1 and MPEG2. In the motion compensation, a motion vector detected by block matching is used.
MPEG 1 and MPEG2 premise basically to increase a compression ratio, and whether the motion vector reproduces real movement precisely is not matter. Because the error of a motion vector appears as the error of a prediction signal generated by the motion compensation, and the error signal between the prediction signal and the input image signal is encoded by DCT. However, in an image display system such as a hold type display, when an interpolation image is formed by the motion compensation using the motion vector that is not a precision, the display image is deteriorated.
On the other hand, detection methods of high precision are thought since it is required in MPEG 4 to reproduce actual movement using the motion vector. For example, Mr. Tei et al. (Nippon Hoso Kyokai) provides a method of utilizing a data group of rhombuses formed by a plurality of frames and blocks in Jpn. Pat. Appln. KOKAI Publication 10-304369. This technique uses a principle that a usual image performs a uniform motion (including a stationary state) with a plurality of frames, and can expect an improvement of motion vector detection precision.
In a motion vector detection technique described by Jpn. Pat. Appln. KOKAI Publication 10-304369, a measure for inspecting whether a detected motion vector is right really is not provided. For this reason, when an interpolation image is formed by motion compensation using an error motion vector, the possibility that the display image has deteriorated greatly is still left. Further, a process for a large number of frames is necessary to improve detection precision of a motion vector, resulting in increasing a processing time.